My favorite amusement park is definitely Disneyland, because it has great rides, great stuff, and great atmosphere.

I don't have an actual correction here because the sentence is correct, but "great stuff" is a bit ambiguous. "Stuff" is a very generic word in the English language. The reader will want more detail. What kind of stuff?

However, anthe entrance fee has been increasing in for years, and there is not an annual pass anymore.

You're referring specifically to the entrance fee at Disneyland, so "the" works better than "an".

One day.,

This should connect to the next sentence with a comma.

My favorite amusement park is definitely Disneyland, because it has great rides, great [stuff], and great atmosphere.

stuff = is too general for this context. We don't know if you mean souvenirs, food and drinks, or something else.

However, anthe entrance fee has been increasing in for years, and there is no annual pass anymore.

It's the fee for the park. It is specific to Disneyland.

One day.,

This is part of the next sentence.
(The sentence is so short, you might even omit the comma.)

My favorite amusement park is definitely Disneyland, because it has great rides, great stuff, and great atmosphere.

While there is nothing wrong, stuff is a very general word for anything. It is not common to list it alongside specific things like rides or atmosphere.
But you may use it like "etc." at the end. For example, "it has great rides, atmosphere, and stuff." This implies there are other things but you do not want to list them all.

However, anthe entrance fee has been increasing in forrecent years, and there is no annual pass anymore.

When you use "an" it feels like you have no particular entrance fee in mind, like some random entrance fee somewhere is being increased. "The" will link the entrance fee to the context you are currently talking about, so readers will know it is referring to Disneyland's.